The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives investigators continued to look into what sparked the flames Thursday as crews work to secure the site to make sure there is no danger of debris falling into the streets or onto people.

Towering flames torched the apartment building and left burned debris structurally unstable, forcing 250 residents at a neighboring apartment building to evacuate, according to fire officials.

Residents were allowed back into their apartments on Friday.

The blaze, which sent flames shooting into the air over the area of Galindo Street and Concord Boulevard, was pronounced under control after an hours-long onslaught from firefighters, but the building is considered to be a total loss with approximately $55 million in damages.

"We look forward to everyone in the city working together, and that's our name: Concord. We live in concordance with one another. We look out for one another," said Concord Mayor Edi Birsan at a news conference Wednesday afternoon.

"We look forward to everyone in the city working together, and that's our name: Concord. We live in concordance with one another. We look out for one another," said Concord Mayor Edi Birsan at a news conference Wednesday afternoon.